The demand for wireless communication for high-speed data communication in addition to voice communication is growing at a fast rate. As this demand continues to grow, systems that are capable of providing both high efficiency and high performance will be increasingly desirable. Multiple Input/Multiple Output (MIMO) systems employ multiple transmitter antennas that transmit to multiple receiver antennas over a wireless channel. Since multiple independent data streams are simultaneously transmitted using the same frequency band, MIMO systems are spectrally highly efficient and, as a result, a higher data throughput is achievable as compared to a single antenna system.
As in all wireless system, the propagation channel is subject to various time-variant channel conditions, or qualities, that cause the amplitude and phase of the received signal to vary. The capacity of the channel is determined, in part, by these channel qualities determined at the receiver end of a wireless system and this channel capacity, when provided to the transmitter, can be used for determining the maximum rate at which the transmitter can transmit a signal to the receiver via that channel. In a MIMO system, each of the multiple transmitter antennas transmits a data stream to the multiple receiver antennas over what can be considered a separate channel. The resultant received signal vector at each receiver antenna is, therefore, a combination of the data streams transmitted by all of the transmitter antennas. Determining the channel qualities of each data stream is thus very difficult. In the prior art, therefore, where channel capacity has been used as the metric for determining a maximum transmission rate at which to transmit the multiple data streams, the capacity of the channel as a whole between the transmitter and the receiver antennas has been determined using overall channel qualities. This overall capacity has then been used to determine a single maximum transmission rate for transmitting each of the data streams. Disadvantageously, this single maximum transmission rate may not optimize usage of the individual channels on which the multiple transmitter antennas are transmitting.